Just Andy's RSA implementation

This is the RSA essence of PR PyMVPA/PyMVPA#121. I took it out, because the original pull request is massive and hard to review. In addition lots of things are intertwined in it.

Here is just the RSA. The test pass in general, but four assertions fail due to transposed shape of the results. I don't know whether there is a "fix" for that in the rest of the original PR, or whether it is just a mistake.

@andycon Could you please have a look at the test failures -- I'll do line comments to pin-point the failures.